Loss of functional skeletal muscle due to traumatic injury, tumor excision, etc., produces a physiological deficit for which there is still no effective clinical treatment. Tissue engineering of skeletal muscle in vitro for functional tissue replacement in vivo may provide a potential therapeutic solution to this unmet medical need. In fact, significant progress has been made during last 15 years in understanding some of the basic requirements for creating tissue engineered skeletal muscle constructs in vitro. Early studies necessarily focused mainly on the production of highly differentiated muscle constructs and characterizing their properties in terms of response to stretch and other mechanical stimulation in a 2-D tissue culture system (Vandenburgh, Mechanical forces and their second messengers in stimulating cell growth in vitro. Am J. Physiol. 262(3 Pt 2):R350-5 (March 1992); Mechanical stimulation of skeletal muscle generates lipid-related second messengers by phospholipase activation. J Cell Physiol. 155(1):63-71 (April 1993).
The majority of recent work on 3-D cultures of skeletal muscle myoblasts has been performed using gel-based matrix and mechanical strainers; as biodegradable scaffolds are thought to possess too much of a development barrier (both structural and nutritional) to clinical development. Recently, 3-D cultures of myoblasts have been successfully established and isometric contractile responses in these 3-D constructs, termed myoids, were measured (Dennis R G, Kosnik P E. Excitability and isometric contractile properties of mammalian skeletal muscle constructs engineered in vitro. In Vitro Cell and Dev Biol Animal. 36:327-335 (2000)). Additionally, fibrin-based gels were suggested as another novel method to engineer 3-D functional muscle tissue. The latter achieved muscle structures of 100-500 μm diameter with measured maximal tetanic force of 805.8±55 μN (Huang Y et al., Rapid formation of functional muscle in vitro using fibrin gels. J Appl Physiol 98: 706-713 (2005)). In short, tissue engineered 3-D skeletal muscle constructs composed of collagen or fibrin gels have clearly improved the understanding of skeletal muscle organogenesis and provide a reasonable model for studying the developmental physiology of skeletal muscle micro-structures in vitro.
However, while muscle constructs developed with synthetic scaffolds can support the contractile portion of the muscle tissue, and furthermore, can be maintained in culture for several months, this approach still has significant limitations for clinical utility. For example, implantation of tissue engineered skeletal muscle constructs will require that they be of relevant size and mechanical strength to be amenable to the rigors of the requisite surgical procedures. Clearly, gel-based constructs are currently too small and too fragile for such surgical manipulatation.
As such, one of the major barriers to engineering clinically applicable functional muscle tissues for reconstructive procedures is the lack of a bioreactor system and methodology that would accelerate cellular organization, tissue formation and function.